March 4, 2017

On February 26, 2017, the skies above Argentina dimmed and the landscape darkened as the Moon moved in front of the Sun, partially blocking its rays. The same thing happened that day in Chile and Angola, as a “ring of fire” (annular eclipse) appeared over the South Atlantic.

An annular eclipse occurs when the Moon passes in front of the Sun but is too far from Earth to completely obscure it. This geometry leaves the Sun’s edges exposed in a red-orange ring. NASA satellites caught several earthly views of the event.

The animation above was assembled from three images acquired on February 26 by NASA’s Earth Polychromatic Imaging Camera (EPIC), a four-megapixel charge-coupled device (CCD) and Cassegrain telescope on the DSCOVR satellite. In that view, both the Earth and the lunar shadow move.

The animation below shows a static view of Earth and the progression of the eclipse shadow. It is composed from 13 separate images acquired by the Moderate Resolution Imaging Spectroradiometer (MODIS) instruments on NASA’s Aqua and Terra satellites, as well as the Visible Infrared Imaging Radiometer Suite (VIIRS) sensor on the Suomi NPP satellite. Each satellite follows the same orbital path but passes over points on Earth at slightly different times in a two-hour span. (Click here for a simple animation of the eclipse shadow path.)

But the February event will soon be eclipsed, so to speak, by another one. On August 21, 2017, a total solar eclipse will cross the entire continental United States for the first time in nearly four decades. The total eclipse will take about 90 minutes to cross from Oregon to South Carolina. During that time, 11 NASA-funded science teams will gather observations of the Sun’s tenuous atmosphere (corona)—which is too faint to see next to the bright solar disk—and of how the eclipse affects Earth and its atmosphere.

“When the Moon blocks out the Sun during a total eclipse, those regions of Earth that are in the direct path of totality become dark as night for almost three minutes,” said Steve Clarke, director of NASA’s Heliophysics Division, in an earlier interview. “This will be one of the best-observed eclipses to date, and we plan to take advantage of this unique opportunity to learn as much as we can about the Sun and its effects on Earth.”

This NASA/ESA Hubble Space Telescope image showcases the remarkable galaxy UGC 12591. Classified as an S0/Sa galaxy, UGC 12591 sits somewhere between a lenticular and a spiral. It lies just under 400 million light-years away from us in the westernmost region of the Pisces–Perseus Supercluster, a long chain of galaxy clusters that stretches out for 250 million light-years — one of the largest known structures in the cosmos.

The galaxy itself is also extraordinary: it is incredibly massive. The galaxy and its halo together contain several hundred billion times the mass of the Sun; four times the mass of the Milky Way. It also whirls round extremely quickly, rotating at speeds of up to 1.8 million kilometres per hour!

Observations with Hubble are helping astronomers to understand the mass of UGC 1259, and to determine whether the galaxy simply formed and grew slowly over time, or whether it might have grown unusually massive by colliding and merging with another large galaxy at some point in its past.

March 3, 2017

Mosaic of the Valles Marineris hemisphere of Mars projected into point perspective, a view similar to that which one would see from a spacecraft. The distance is 2500 kilometers from the surface of the planet, with the scale being .6km/pixel. The mosaic is composed of 102 Viking Orbiter images of Mars. The center of the scene (lat -8, long 78) shows the entire Valles Marineris canyon system, over 2000 kilometers long and up to 8 kilometers deep, extending form Noctis Labyrinthus, the arcuate system of graben to the west, to the chaotic terrain to the east. Many huge ancient river channels begin from the chaotic terrain from north-central canyons and run north. The three Tharsis volcanoes (dark red spots), each about 25 kilometers high, are visible to the west. South of Valles Marineris is very ancient terrain covered by many impact craters.

Considered to be the first cold super Earth, this exoplanet began to form a Jupiter-like core of rock and ice, but couldn’t grow fast enough in size. Its final mass is five times that of Earth.

Using a relatively new planet-hunting technique that can spot worlds one-tenth the mass of our own, researchers have discovered a potentially rocky, icy body that may be the smallest planet yet found orbiting a star outside our solar system.

The discovery suggests the technique, gravitational microlensing, may be an exceptional technology for finding distant planets with traits that could support life.

"This important research, partly funded by NASA, is providing us the opportunity to search for planets in habitable environments," said Zlatan Tsvetanov, Terrestrial Planet Finder program scientist at NASA Headquarters, Washington. "The results successfully demonstrate the power of gravitational microlensing, currently the only ground-based technique with the sensitivity to detect extrasolar Earth-size planets on Earth-like orbits, and provide an important clue of the ubiquity of small planets."

Located more than 20,000 light years away in the constellation Sagittarius, close to the center of our Milky Way galaxy, planet OGLE-2005-BLG-390Lb is approximately five-and-a-half times the mass of Earth.

Orbiting a star one-fifth the mass of the sun at a distance almost three times that of Earth's orbit, the newly discovered planet is frigid -- the estimated surface temperature is -364 degrees Fahrenheit.

Although astronomers doubt this cold body could sustain organisms, researchers believe gravitational microlensing will bring opportunities for observing other rocky planets in the "habitable zones" of stars where temperatures are perfect for maintaining liquid water and spawning life.

The discovery, authored by 73 collaborators from 32 institutions, appears in the January 26 issue of the journal Nature.

The Optical Gravitational Lensing Experiment (OGLE) project telescopes first observed the lensing event on July 11, 2005. In an attempt to catch microlensing events as they occur, OGLE scans most of the central Milky Way each night, discovering more than 500 microlensing events per year. But to detect the signature of low-mass planets, astronomers must observe these events much more frequently than OGLE’s one survey per night.

So, when OGLE detected the July 11 lensing, its early warning system alerted fellow astronomers across the globe to microlensing event OGLE-2005-BLG-390 (for the 390th Galactic bulge OGLE discovered in 2005). At that point, though, no one knew a planet would emerge.

"The only way to realize the full scientific benefit of our observations is to share the data with our competition," said co-author Bohdan Paczynski of Princeton University, Princeton, New Jersey, and one of the OGLE co-founders.

The telescopes of Probing Lensing Anomalies NETwork (PLANET) and RoboNet tracked the July 11 episode to completion, providing the data that confirmed the presence of a previously unknown planet. The telescopes collect observations more frequently in an attempt to detect the microlensing signature of planets.

"This discovery was possible because the sun never rises on the PLANET collaboration," said lead author and PLANET researcher Jean-Philippe Beaulieu of the Institut d’Astrophysique de Paris, France. "The global nature of the PLANET collaboration was crucial for obtaining data throughout the 24-hour planetary signal," he said.

Ironically, when preparing the final report, the researchers discovered that during its test runs, the new Microlensing Observations in Astrophysics (MOA) telescope, MOA-2, had taken additional measurements of the lensing event. The 6-foot aperture telescope has a wider field-of-view than the OGLE telescope, enabling it to observe 100 million stars many times per night. MOA-2 is one of several recent and future advancements that gravitational microlensing proponents hope will greatly increase the number of Earth-like planet discoveries.

"The new discovery provides a strong hint that low-mass planets may be much more common than Jupiters," said co-author and PLANET researcher David Bennett of the University of Notre Dame, South Bend, Indiana. Until recently, most extrasolar planets researchers have found have been Jupiter-like gas giants. "Microlensing should have discovered dozens of Jupiters by now if they were as common as these five-Earth-mass planets. This illustrates the primary strength of the gravitational microlensing method: its ability to find planets of low-mass."

Low-mass planets can yield signals that are too weak to detect with other methods. With microlensing, the signals of low-mass planets are rare but not weak. Thus, scientists say, the rate of low-mass planet discoveries should increase dramatically if more microlensing events can be searched for planetary signals

The International Space Station is featured in this image photographed by an STS-132 crew member on space shuttle Atlantis after the station and shuttle began their post-undocking relative separation. Undocking of the two spacecraft occurred at 10:22 a.m. (CDT) on May 23, 2010, ending a seven-day stay that saw the addition of a new station module, replacement of batteries and resupply of the orbiting outpost.

The events surrounding the Big Bang were so cataclysmic that they left an indelible imprint on the fabric of the cosmos. We can detect these scars today by observing the oldest light in the Universe. As it was created nearly 14 billion years ago, this light — which exists now as weak microwave radiation and is thus named the cosmic microwave background (CMB) — has now expanded to permeate the entire cosmos, filling it with detectable photons.

The CMB can be used to probe the cosmos via something known as the Sunyaev-Zel’dovich (SZ) effect, which was first observed over 30 years ago. We detect the CMB here on Earth when its constituent microwave photons travel to us through space. On their journey to us, they can pass through galaxy clusters that contain high-energy electrons. These electrons give the photons a tiny boost of energy. Detecting these boosted photons through our telescopes is challenging but important — they can help astronomers to understand some of the fundamental properties of the Universe, such as the location and distribution of dense galaxy clusters.

The NASA/ESA Hubble Space Telescope observed one of most massive known galaxy clusters, RX J1347.5–1145, seen in this Picture of the Week, as part of the Cluster Lensing And Supernova survey with Hubble (CLASH). This observation of the cluster, 5 billion light-years from Earth, helped the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile to study the cosmic microwave background using the thermal Sunyaev-Zel’dovich effect. The observations made with ALMA are visible as the blue-purple hues.

A swing high above Saturn by NASA's Cassini spacecraft revealed this stately view of the golden-hued planet and its main rings. The view is in natural color, as human eyes would have seen it. This mosaic was made from 36 images in three color filters obtained by Cassini's imaging science subsystem on Oct. 10, 2013. The observation and resulting image mosaic were planned as one of three images for Cassini's 2013 Scientist for a Day essay contest.

Saturn sports differently colored bands of weather in this image. For instance, a bright, narrow wave of clouds around 42 degrees north latitude appears to be some of the turbulent aftermath of a giant storm that reached its violent peak in early 2011. The mysterious six-sided weather pattern known as the hexagon is visible around Saturn's north pole.

When Cassini arrived in 2004, more of the northern hemisphere sported a bluish hue and it was northern winter. The golden tones dominated the southern hemisphere, where it was southern summer. But as the seasons have turned and northern spring is in full swing, the colors have begun to change in each hemisphere as well. Golden tones have started to dominate in the northern hemisphere and the bluish color in the north is now confined to a tighter circle around the north pole. The southern hemisphere has started getting bluer, too.

The rings shown here include Saturn's main rings. The rings known as the C, B and A rings -- listed here in order of closeness to Saturn -- are easily seen. The F ring is also there, but not easily seen without enhancing the contrast of the image. (Rings were named in order of their discovery rather than their position around Saturn.) The rings also cast a shadow on Saturn at the limb of the planet in the lower right quadrant.

March 2, 2017

DG CVn, a binary consisting of two red dwarf stars shown here in an artist's rendering, unleashed a series of powerful flares seen by NASA's Swift. At its peak, the initial flare was brighter in X-rays than the combined light from both stars at all wavelengths under typical conditions.

On April 23, 2014, NASA's Swift satellite detected the strongest, hottest, and longest-lasting sequence of stellar flares ever seen from a nearby red dwarf star. The initial blast from this record-setting series of explosions was as much as 10,000 times more powerful than the largest solar flare ever recorded.

"We used to think major flaring episodes from red dwarfs lasted no more than a day, but Swift detected at least seven powerful eruptions over a period of about two weeks," said Stephen Drake, an astrophysicist at NASA's Goddard Space Flight Center in Greenbelt, Maryland, who gave a presentation on the "superflare" at the August meeting of the American Astronomical Society’s High Energy Astrophysics Division. "This was a very complex event."

At its peak, the flare reached temperatures of 360 million degrees Fahrenheit (200 million Celsius), more than 12 times hotter than the center of the Sun.

The "superflare" came from one of the stars in a close binary system known as DG Canum Venaticorum, or DG CVn for short, located about 60 light-years away. Both stars are dim red dwarfs with masses and sizes about one-third of our Sun's. They orbit each other at about three times Earth's average distance from the Sun, which is too close for Swift to determine which star erupted.

"This system is poorly studied because it wasn't on our watch list of stars capable of producing large flares," said Rachel Osten, an astronomer at the Space Telescope Science Institute in Baltimore and a deputy project scientist for NASA's James Webb Space Telescope, now under construction. "We had no idea DG CVn had this in it."

Most of the stars lying within about 100 light-years of the solar system are, like the Sun, middle-aged. But a thousand or so young red dwarfs born elsewhere drift through this region, and these stars give astronomers their best opportunity for detailed study of the high-energy activity that typically accompanies stellar youth. Astronomers estimate DG CVn was born about 30 million years ago, which makes it less than 0.7 percent the age of the solar system.

Stars erupt with flares for the same reason the Sun does. Around active regions of the star's atmosphere, magnetic fields become twisted and distorted. Much like winding up a rubber band, these allow the fields to accumulate energy. Eventually a process called magnetic reconnection destabilizes the fields, resulting in the explosive release of the stored energy we see as a flare. The outburst emits radiation across the electromagnetic spectrum, from radio waves to visible, ultraviolet and X-ray light.

At 5:07 p.m. EDT on April 23, the rising tide of X-rays from DG CVn's superflare triggered Swift's Burst Alert Telescope (BAT). Within several seconds of detecting a strong burst of radiation, the BAT calculates an initial position, decides whether the activity merits investigation by other instruments and, if so, sends the position to the spacecraft. In this case, Swift turned to observe the source in greater detail, and, at the same time, notified astronomers around the globe that a powerful outburst was in progress.

"For about three minutes after the BAT trigger, the superflare's X-ray brightness was greater than the combined luminosity of both stars at all wavelengths under normal conditions," noted Goddard's Adam Kowalski, who is leading a detailed study on the event. "Flares this large from red dwarfs are exceedingly rare."

The star's brightness in visible and ultraviolet light, measured both by ground-based observatories and Swift's Optical/Ultraviolet Telescope, rose by 10 and 100 times, respectively. The initial flare's X-ray output, as measured by Swift's X-Ray Telescope, puts even the most intense solar activity recorded to shame.

The largest solar explosions are classified as extraordinary, or X class, solar flares based on their X-ray emission. "The biggest flare we've ever seen from the Sun occurred in November 2003 and is rated as X 45," explained Drake. "The flare on DG CVn, if viewed from a planet the same distance as Earth is from the Sun, would have been roughly 10,000 times greater than this, with a rating of about X 100,000."

But it wasn't over yet. Three hours after the initial outburst, with X-rays on the downswing, the system exploded with another flare nearly as intense as the first. These first two explosions may be an example of "sympathetic" flaring often seen on the Sun, where an outburst in one active region triggers a blast in another.

Over the next 11 days, Swift detected a series of successively weaker blasts. Osten compares the dwindling series of flares to the cascade of aftershocks following a major earthquake. All told, the star took a total of 20 days to settle back to its normal level of X-ray emission.

How can a star just a third the size of the Sun produce such a giant eruption? The key factor is its rapid spin, a crucial ingredient for amplifying magnetic fields. The flaring star in DG CVn rotates in under a day, about 30 or more times faster than our Sun. The Sun also rotated much faster in its youth and may well have produced superflares of its own, but, fortunately for us, it no longer appears capable of doing so.

Astronomers are now analyzing data from the DG CVn flares to better understand the event in particular and young stars in general. They suspect the system likely unleashes numerous smaller but more frequent flares and plan to keep tabs on its future eruptions with the help of NASA's Swift.

This colourful stripe of stars, gas, and dust is actually a spiral galaxy named NGC 1055. Captured here by ESO’s Very Large Telescope (VLT), this big galaxy is thought to be up to 15 percent larger in diameter than the Milky Way. NGC 1055 appears to lack the whirling arms characteristic of a spiral, as it is seen edge-on. However, it displays odd twists in its structure that were probably caused by an interaction with a large neighbouring galaxy.

Spiral galaxies throughout the Universe take on all manner of orientations with respect to Earth. We see some from above (as it were) or “face-on” — a good example of this being the whirlpool-shaped galaxy NGC 1232. Such orientations reveal a galaxy’s flowing arms and bright core in beautiful detail, but make it difficult to get any sense of a three-dimensional shape.

We see other galaxies, such as NGC 3521, at angles. While these tilted objects begin to reveal the three-dimensional structure within their spiral arms, fully understanding the overall shape of a spiral galaxy requires an edge-on view — such as this one of NGC 1055.

When seen edge-on, it is possible to get an overall view of how stars — both new patches of starbirth and older populations — are distributed throughout a galaxy, and the “heights” of the relatively flat disc and the star-loaded core become easier to measure. Material stretches away from the blinding brightness of the galactic plane itself, becoming more clearly observable against the darker background of the cosmos.

Such a perspective also allows astronomers to study the overall shape of a galaxy’s extended disc, and to study its properties. One example of this is warping, which is something we see in NGC 1055. The galaxy has regions of peculiar twisting and disarray in its disc, likely caused by interactions with the nearby galaxy Messier 77. This warping is visible here; NGC 1055’s disc is slightly bent and appears to wave across the core.

NGC 1055 is located approximately 55 million light-years away in the constellation of Cetus (The Sea Monster). This image was obtained using the FOcal Reducer and low dispersion Spectrograph 2 (FORS2) instrument mounted on Unit Telescope 1 (Antu) of the VLT, located at ESO’s Paranal Observatory in Chile. It hails from ESO’s Cosmic Gems programme, an outreach initiative that produces images of interesting, intriguing or visually attractive objects using ESO telescopes for the purposes of education and outreach.

February 28, 2017

This artist's animation shows the view from a hypothetical moon in orbit around the first known planet to reside in a tight-knit triple-star system. The gas giant planet, discovered using the Keck I telescope atop Mauna Kea in Hawaii, zips around a single star that is orbited by a nearby pair of pirouetting stars.

A NASA-funded astronomer has discovered a world where the sun sets over the horizon, followed by a second sun and then a third. The new planet, called HD 188753 Ab, is the first known to reside in a classic triple-star system.

"The sky view from this planet would be spectacular, with an occasional triple sunset," said Dr. Maciej Konacki (MATCH-ee Konn-ATZ-kee) of the California Institute of Technology, Pasadena, Calif., who found the planet using the Keck I telescope atop Mauna Kea mountain in Hawaii. "Before now, we had no clues about whether planets could form in such gravitationally complex systems."

The finding suggests that planets are more robust than previously believed.

"This is good news for planets," said Dr. Shri Kulkarni, who oversees Konacki's research at Caltech. "Planets may live in all sorts of interesting neighborhoods that, until now, have gone largely unexplored." Kulkarni is the interdisciplinary scientist for NASA's planned SIM PlanetQuest mission, which will search for signs of Earth-like worlds.

Systems with multiple stars are widespread throughout the universe, accounting for more than half of all stars. Our Sun's closest star, Alpha Centauri, is a member of a trio.

"Multiple-star systems have not been popular planet-hunting grounds," said Konacki. "They are difficult to observe and were believed to be inhospitable to planets."

The new planet belongs to a common class of extrasolar planets called "hot Jupiters," which are gas giants that zip closely around their parent stars. In this case, the planet whips every 3.3 days around a star that is circled every 25.7 years by a pirouetting pair of stars locked in a 156-day orbit.

The circus-like trio of stars is a cramped bunch, fitting into the same amount of space as the distance between Saturn and our Sun. Such tight living quarters throw theories of hot Jupiter formation into question. Astronomers had thought that hot Jupiters formed far away from their parent stars, before migrating inward.

"In this close-knit system, there would be no room at the outskirts of the parent star system for a planet to grow," said Konacki.

Previously, astronomers had identified planets around about 20 binary stars and one set of triple stars. But the stars in those systems had a lot of space between them. Most multiple-star arrangements are crowded together and difficult to study.

Konacki overcame this challenge using a modified version of the radial velocity, or "wobble," planet-hunting technique. In the traditional wobble method, a planet's presence is inferred by the gravitational tug, or wobble, it induces in its parent star. The strategy works well for single stars or far-apart binary and triple stars, but could not be applied to close-star systems because the stars' light blends together.

By developing detailed models of close-star systems, Konacki was able to tease apart the tangled starlight. This allowed him to pinpoint, for the first time, the tug of a planet on a star snuggled next to other stars. Of 20 systems examined so far, HD 188753, located 149 light-years away, was the only one found to harbor a planet.

Hot Jupiters are believed to form out of thick disks, or "doughnuts," of material that swirl around the outer fringes of young stars. The disk material clumps together to form a solid core, then pulls gas onto it. Eventually, the gas giant drifts inward. The discovery of a world under three suns contradicts this scenario. HD 188753 would have sported a truncated disk in its youth, due to the disruptive presence of its stellar companions. That leaves no room for HD 188753's planet to form, and raises a host of new questions.

The masses of the three stars in HD 188753 system range from two-thirds to about the same mass as our Sun. The planet is slightly more massive than Jupiter.

A picturesque line of thunderstorms and numerous circular cloud patterns filled the view as the International Space Station (ISS) Expedition 20 crew members looked out at the limb (blue line on the horizon) of the Earth. The region shown in the astronaut photograph (top image) includes an unstable, active atmosphere forming a large area of cumulonimbus clouds in various stages of development. The crew was looking west-southwest from the Amazon Basin, along the Rio Madeira toward Bolivia when the image was taken.

The semi-circular cloud patterns near the center of the astronaut photograph may be detected in a Geostationary Operational Environmental Satellite (GOES) infrared satellite image of the region (bottom image, yellow rectangle) acquired about 20 minutes earlier than the astronaut photograph. The distinctive circular patterns of the clouds in the astronaut photograph are likely caused by the aging of thunderstorms. Such ring structures often form during the final stages of storms’ development as their centers collapse.

Sunglint—the mirror-like reflection of sunlight off a water surface directly back to the camera onboard the ISS—is visible on the waters of the Rio Madeira and Lago Acara in the Amazon Basin. Widespread haze over the basin gives the reflected light an orange hue. The Rio Madeira flows northward and joins the Amazon River on its path to the Atlantic Ocean. A large smoke plume near the bottom center of the image may be one source of the haze.

February 27, 2017

This artist’s impression shows the planet orbiting the Sun-like star HD 85512 in the southern constellation of Vela (The Sail). This planet is about 3.6 times as massive as the Earth and lies at the edge of the habitable zone around the star, where liquid water, and perhaps even life, could potentially exist.

Twenty years ago astronomers discovered the first planet around a Sun-like star, 51 Pegasi b. And in the last 20 years, astronomers have discovered thousands of new exotic worlds, begun to characterize atmospheres of faraway planets, and are developing cutting-edge technology to launch us on our search for alien life. Planets with two suns, rogue planets with no star, close cousins to planet Earth. This is the story of the pioneers in planet-hunting and how those who have followed are now poised to answer one of humanity’s most ancient questions: is there life elsewhere in the Universe?

By using the full power of the Very Large Telescope Interferometer an international team of astronomers has discovered exozodiacal light close to the habitable zones around nine nearby stars. This light is starlight reflected from dust created as the result of collisions between asteroids, and the evaporation of comets. The presence of such large amounts of dust in the inner regions around some stars may pose an obstacle to the direct imaging of Earth-like planets in the future.

Using the Very Large Telescope Interferometer (VLTI) in near-infrared light, the team of astronomers observed 92 nearby stars to probe exozodiacal light from hot dust close to their habitable zones and combined the new data with earlier observations. Bright exozodiacal light, created by the glowing grains of hot exozodiacal dust, or the reflection of starlight off these grains, was observed around nine of the targeted stars.

From dark clear sites on Earth, zodiacal light looks like a faint diffuse white glow seen in the night sky after the end of twilight, or before dawn. It is created by sunlight reflected off tiny particles and appears to extend up from the vicinity of the Sun. This reflected light is not just observed from Earth but can be observed from everywhere in the Solar System.

The glow being observed in this new study is a much more extreme version of the same phenomenon. While this exozodiacal light — zodiacal light around other star systems — had been previously detected, this is the first large systematic study of this phenomenon around nearby stars.

In contrast to earlier observations the team did not observe dust that will later form into planets, but dust created in collisions between small planets of a few kilometres in size — objects called planetesimals that are similar to the asteroids and comets of the Solar System. Dust of this kind is also the origin of the zodiacal light in the Solar System.

“If we want to study the evolution of Earth-like planets close to the habitable zone, we need to observe the zodiacal dust in this region around other stars,” said Steve Ertel, lead author of the paper, from ESO and the University of Grenoble in France. “Detecting and characterising this kind of dust around other stars is a way to study the architecture and evolution of planetary systems.”

Detecting faint dust close to the dazzling central star requires high resolution observations with high contrast. Interferometry — combining light collected at the exact same time at several different telescopes — performed in infrared light is, so far, the only technique that allows this kind of system to be discovered and studied.

By using the power of the VLTI and pushing the instrument to its limits in terms of accuracy and efficiency, the team was able to reach a performance level about ten times better than other available instruments in the world.

For each of the stars the team used the 1.8-metre Auxiliary Telescopes to feed light to the VLTI. Where strong exozodiacal light was present they were able to fully resolve the extended discs of dust, and separate their faint glow from the dominant light of the star.

By analysing the properties of the stars surrounded by a disc of exozodiacal dust, the team found that most of the dust was detected around older stars. This result was very surprising and raises some questions for our understanding of planetary systems. Any known dust production caused by collisions of planetesimals should diminish over time, as the number of planetesimals is reduced as they are destroyed.

The sample of observed objects also included 14 stars for which the detection of exoplanets has been reported. All of these planets are in the same region of the system as the dust in the systems showing exozodiacal light. The presence of exozodiacal light in systems with planets may create a problem for further astronomical studies of exoplanets.

Exozodiacal dust emission, even at low levels, makes it significantly harder to detect Earth-like planets with direct imaging. The exozodiacal light detected in this survey is a factor of 1000 times brighter than the zodiacal light seen around the Sun. The number of stars containing zodiacal light at the level of the Solar System is most likely much higher than the numbers found in the survey. These observations are therefore only a first step towards more detailed studies of exozodiacal light.

“The high detection rate found at this bright level suggests that there must be a significant number of systems containing fainter dust, undetectable in our survey, but still much brighter than the Solar System’s zodiacal dust,” explains Olivier Absil, co-author of the paper, from the University of Liège. “The presence of such dust in so many systems could therefore become an obstacle for future observations, which aim to make direct images of Earth-like exoplanets.”

The NASA/ESA Hubble Space Telescope has captured this image of PGC 10922, an example of a lenticular galaxy — a galaxy type that lies on the border between ellipticals and spirals.

Seen face-on, the image shows the disc and tightly-wound spiral structures of dark dust encircling the bright centre of the galaxy. There is also a remarkable outer halo of faint wide arcs or shells extending outwards, covering much of the picture. These are likely to have been formed by a gravitational encounter or even a merger with another galaxy. Some dust also appears to have escaped from the central structure and has spread out across the inner shells.

An extraordinarily rich background of more remote galaxies can also be seen in the image.